Electricity is commonly delivered from electricity suppliers to consumers in the form of alternating current (AC) at a certain fundamental frequency, e.g., 60 Hz in the U.S. The consumption of electricity, e.g., three-phase AC, is commonly measured by power meters. When the load of an power supply system includes non-linear components, harmonic frequencies, other than the fundamental frequency, might be created on the power supply line. Additionally, when the load is not purely resistive, the waveform of voltage V may lead or lag the waveform of current I in time or have a phase offset in the frequency domain.
Electrical power at each frequency may include three components: apparent power (Papp), active power (Pact), and reactive power (Preact). The apparent power Papp(w) for a particular angular frequency w may be defined as the product of magnitudes of voltage V(w) and current I(w), i.e., P(w)=V(w)*I(w). The active power Pact(w) may be defined as the capacity of the load at a particular time or the energy that flows from power source to the load. The reactive power Preactive(W) may be defined as the energy that is bounced back from the load to the source. If the phase offset between current and voltage is φ, then Pact(w)=Papp(w)*|Cos(φ)| and Preact(w)=Papp(w)*|Sin(φ)|.
When the number of non-linear loads, e.g., switching power supplies, increases, a larger amount of harmonic content may be present in the power system. These harmonics may limit the effectiveness of the power system to deliver electrical power from a source to a load. The combination of digital signal processing (DSP) and high performance analog to digital converters (ADCs) at low prices provides electrical power suppliers with new options for improving and optimizing electrical power meters. The owner suppliers may want to know how much electrical power is delivered not only at the fundamental frequency but also at harmonic frequencies. Also, the supplier of energy may want to know about the existence of harmonics because these harmonics have the potential of damaging some delivery equipment (e.g., wires and transformers).
Current techniques for computing power at a fundamental frequency or harmonic frequencies are mostly based on phase locked loop (PLL) and band-pass filters. Other methods may use FFT transform. These methods and devices suffer from a prolonged calculation time. In particular, level of harmonics is mostly unknown and PLL performance degrades when trying to lock on signals that get closer and closer to the sampling frequency. In view of current techniques for measuring power consumptions, there is a need for computing power simultaneously at the fundamental frequency or at a plurality of harmonic frequencies in near real time.